Pressure-compensated, directly controlled valve

ABSTRACT

The invention relates to a valve for high-pressure hydraulics, having a valve bore provided in a valve housing in which bore at least one valve seat dividing a guide on the high-pressure side of the valve bore from a guide on the low-pressure side of the valve bore and a valve needle actuatable directly by an actuator which needle is guided in the valve bore and has at least one sealing face which can cooperate with the at least one valve seat in which the valve needle is constructed in multiple parts and, in the region of the guide on the low-pressure side, has at least one sleeve.

FIELD OF THE INVENTION

To supply fuel to combustion chambers of internal combustion engines,injection systems for injecting fuel are used whose injectors or valvesare exposed to extremely high pressures. Especially valves in the areaof Diesel injection technology are conceived such that they canwithstand high hydraulic pressures. Such Diesel valves operate on eitherthe inward-opening or the outward-opening principle and have extremelyhigh-speed switching. The function that assures that they remain tightis determined in such Diesel valves in the closed state by minimalleakage and minimal hydraulic forces that act on the valve needle.

If such a valve is used for a fuel injection pump of the distributortype, it serves to provide communication for a pump work chamber with alow-pressure region by way of which fuel is delivered. In this way, thevalve controls not only the delivery of fuel to the pump work chamberduring an intake but also the end of injection, in which by opening thevalve prevents further pressure from building up in the pump workchamber.

BACKGROUND OF THE INVENTION

In Diesel injection valves, it is generally known to minimize thehydraulic forces operative in the opening direction by reducing thepressure engagement faces, which is done by embodying the sealingdiameter as equal to the guide diameter of the valve bore.

In the open state, however, such valves are not pressure-compensated, orat least are only partly pressure-compensated. The consequences are thatpressure waves which build up upon switching of the valves then generatehydraulic forces on the valve needle. Under some circumstances theseundefined forces alter the switching behavior of the valve, which mayresult in a deviation in the injection quantities.

Moreover, the occurrence of so-called cavitation erosion is well known.If to terminate fuel supply or to determine the fuel injection quantitythe valve is opened, a decrease in the pressure in the pump work chambertakes place; previously, this pressure was at a very high level, such as1000 to 1200 bar, and now via the valve opening fuel flows to thelow-pressure region and lowers the pressure. In this outflow, because ofthe high pressure difference between the high-pressure region and thelow-pressure region of the valve, flow separations and so-called flowrecirculations can occur. In them, gas or vapor bubbles are formed inthe fuel. The cause of this is that the static pressure drops below thevapor pressure of the fuel. As soon as the pressure rises again, namelyupon an ensuing implosion, the vapor in the vapor bubbles condenses, andthe fuel strikes the valve housing and the valve member at high speed.This effect is all the more pronounced, the more turbulence there is inthe flow. Such turbulence occurs especially because of the abruptincrease in the cross section downstream of the valve seat, becausethere the flow separates under the influence of strong eddy and vaporbubble development.

Especially in the vicinity of the surrounding walls, under somecircumstances this can cause material damage, known as cavitationerosion, which occurs especially directly downstream of the valve seat.If this erosion spreads to the valve seat itself, over the long termthis leads to malfunctions of the valve.

From the prior art, such as German Patent Disclosure DE 197 17 494 A1,to reduce the danger of cavitation damage it is known to provide anarrowed cross section in the outflow conduit from the chamber locateddownstream of the valve seat. This kind of narrowed cross section isintended to assure that upon inflow of the medium into the chamber, themedium can rapidly build up a pressure so that possible eddy currentsand resultant bubble formation effects are at least reduced. However,the valve known from this reference has the disadvantage that to createthis narrowing of diameter in the fuel connecting line that is embodiedin the valve housing, additional metal-cutting work steps are necessary,which increase the cost for the production process.

Moreover, from German Patent Disclosure DE 199 40 296 A1, a valve for afuel injection pump of the distributor type is known in which thecavitation effects are avoided by providing the valve needle with atleast one guide face that cooperates, in the open state of the valve,with at least one baffle face provided in the valve bore of the valvehousing, in such a way that a flow conduit is embodied that widens at aconstant gradient in the flow direction, beginning at a minimal crosssection in the region of the valve seat. The effect of this gradient isthat the pressure increase is limited to a value that the flow boundarylayer at this baffle face can still absorb, without allowing gas bubblesto be released. However, this kind of valve is not capable of completelyeliminating the effects of cavitation, and moreover requirescomplicated, expensive evaluations in terms of flow technology.Accordingly, the valve has a complicated shape which can be achievedonly at increased cost and expenditure of time.

SUMMARY OF THE INVENTION

With the embodiment proposed according to the invention, cavitationeffects on the one hand and undefined forces on the valve needle on theother can be avoided entirely, so that such a valve can be produced atsubstantially reduced effort and expense. Since as a consequence of thecomplete low-pressure compensation attainable with this valve, thehydraulic forces upon opening of the valve are greatly reduced, theswitching behavior and thus the injection quantity precision of thevalve are improved considerably.

In general, the invention is distinguished in that the valve needle usedhas a multi-part structure, especially such that in the region of theguide on the low side of the valve bore of the valve, at least onesleeve is provided. This sleeve is slipped onto a reduced diameter ofthe valve needle with a narrow element play, preferably 1 to 2 μm, sothat it can easily execute axial motions. Compared to the valve bore,the sleeve itself is guided in turn with a slight element play, onceagain preferably 1 to 2 μm. The sleeve is axially braced relative to thevalve needle by means of at least one elastic element.

In a further feature of the invention, the valve needle has the samediameter on the guide on the high-pressure side of the valve bore as atthe guide on the low-pressure side of the valve bore, where the sleeveis supported in guiding fashion. The effect is that the guide diameterand the sealing diameter are the same size, thereby assuring a completehigh-pressure and low-pressure compensation.

These proposed valve constructions are preferably suitable for Dieselinjection valves of the 2/2-way valve or 3/2-way valve type.

It becomes clear that because of the technically simple realization of amulti-part construction of the valve needle, a definition of theindividual diameters can be accomplished in a simple way, so that theeffects of the pressure compensation in the high-pressure region and thelow-pressure region can be accomplished both when the valve is open andwhen it is closed. The invention makes use of functional principles andcomponents that are technologically simple to achieve.

DRAWING

The invention is described in further detail below in conjunction withthe drawing.

Shown are:

FIG. 1, a variant embodiment of the embodiment proposed according to theinvention for a 2/2-way valve type;

FIG. 2, a first variant embodiment of a 3/2-way valve type;

FIG. 3, a second variant embodiment of the embodiment proposed accordingto the invention of a 3/2-way valve type; and

FIG. 4, a third variant embodiment of the embodiment proposed accordingto the invention of a 3/2-way valve type.

VARIANT EMBODIMENTS

FIG. 1 shows a 2/2-way valve of the embodiment proposed according to theinvention, in particular a 2/2-way Diesel injection valve. It includes avalve needle 1, which is axially guided in a valve bore 3 of a valvehousing 2. The valve needle 1 is actuated directly by an actuator 4, notshown in further detail. It is possible for the valve needle 1 to besolidly joined to the actuator in terms of assembly, and all the variantconstructions known from the prior art, such as a magnet actuator,piezoelectric actuator, and so forth, may be employed.

The valve bore 3 has an inward-opening valve seat 5 (I-valve seat). Thevalve shown in FIG. 1 is shown in its open position. The inward-openingvalve seat 5 divides the valve bore 3 into a high-pressure region and acontrol-pressure or low-pressure region.

The high-pressure region has a first conduit 6, through which fuel isfed into a high-pressure chamber 7 at the intended high pressure. Thevalve bore 3 of the high-pressure region forms a guide 8 on thehigh-pressure side for the valve needle 1.

At the valve needle 1, the seat angle difference in the cone angle ofthe valve housing 2 compared to the valve bore 3 creates the sealingedge 9 of the valve needle 1.

The low-pressure region of the 2/2-way valve has a second conduit 10 forthe control pressure, which discharges into a control chamber 11. In thelow-pressure region, the valve bore 3 forms a guide 12 on thelow-pressure side.

The valve needle 1, in this low-pressure region, has a lesser diameterthan in the high-pressure region. A sleeve 13 is slipped with a veryslight play onto this portion of lesser diameter of the valve needle 1,so that only the most minimal relative motions can be performed by thesleeve 13. The sleeve 13 is supported on a rounded shoulder 14 of thevalve needle 1 by means of an elastic element 15, such as a spring ring.Opposite this elastic element 15, the sleeve 13 is braced on a snap ring16, which is retained in a groove in the valve needle 1. To that end,the sleeve 13 has a chamfer 17, so that the snap ring 16 is received byit in such a way that the sleeve 13 is axially braced; the spring forceof the elastic element 15 on the one hand and a pressure possiblyprevailing in the control chamber 11 on the other create this axialbracing.

It can be seen that for the high-pressure compensation in a closed stateof the 2/2-way valve, the sealing edge 9 of the inward-opening valveseat 5 has the same diameter as the guide diameter of the guide 8 on thehigh-pressure side of the valve needle 1 in the valve bore 3, whileconversely for a low-pressure compensation in an open state of the2/2-way valve, the valve needle 1 has the same diameter at the guide 8on the high-pressure side and at the guide 12 on the low-pressure side.This latter feature is accomplished by providing that the sleeve 13 isdefined with suitable dimensions for the purpose.

Because of the fact that the sleeve 13 in the guide 12 on thelow-pressure side of the valve bore 3 and in the corresponding portionof the valve needle 1 is guided with a very narrow element play, sealingoff of the pressure, prevailing in the control chamber 11, from a return18 is assured.

The valve needle 1 can be introduced from the actuator side into thevalve bore 3, and after that the elastic element 15, sleeve 13 and snapring 16 can be installed from the return side, making for simpleinstallation of the entire assembly of the 2/2-way valve.

FIGS. 2-4 show various variant embodiments of a 3/2-way valve type, inparticular a 3/2-way Diesel injection valve. For characteristics havingthe same function in the various variant embodiments, the same referencenumerals are used.

FIG. 2 shows a first variant embodiment of a 3/2-way valve type. Thisvalve has a second valve seat in the form of a slide seat 19 in thelow-pressure region. Accordingly, the opening cross section is composedof the total stroke of the valve needle 1, minus the overlap of theslide seat 19 in a closed state. A third conduit 20 for the return intothe control chamber 11 discharges into the low-pressure region of thevalve.

In the portion on the low-pressure side, the valve needle 1 has alengthened diameter. A first sleeve 21 is slipped onto this portion,directly abutting the rounded shoulder 14. A second sleeve 22 is alsoprovided, and the elastic element 15, that is, the spring disk, isinserted between the first sleeve 21 and the second sleeve 22. Thesecond sleeve 22 in turn, on the end opposite the elastic element 15,has a chamfer 17, in which the snap ring 16, retained in a groove, isreceived on the valve needle 1.

The first sleeve 21 and the second sleeve 22 are the same in their outerdiameter and are slipped onto the portion of lesser diameter of thevalve needle 1 with a very narrow element play, preferably of 1 to 2 μm.The first sleeve 21 can in turn be guided with very narrow element playin the bore of the slide 19. The second sleeve 22 is furthermore fittedwith a likewise very narrow element play in the guide 12 on thelow-pressure side of the valve bore 3. The leakage from the closed slideseat 19 is determined by the axial overlap of the sleeve 21 in the boreof this slide seat 19 and by the very slight element play.

For the complete high-pressure compensation on the one hand andlow-pressure compensation on the other of the slide seat 19, the outerdiameter of the sleeve 21 is equal to the diameter of the guide 8 on thehigh-pressure side of the valve needle 1 and equal to the outer diameterof the second sleeve 22.

It is understood that this variant embodiment of a 3/2-way valve is alsoconceivable with only a single sleeve, as has been described inconjunction with the embodiment of a 2/2-way valve shown in FIG. 1.

In FIG. 3, a second variant embodiment of a 3/2-way valve is shown,which instead of a slide seat has an outward-opening valve seat 23(A-valve seat) in the low-pressure region of the valve.

A first sleeve 24 is guided with a narrow guide play on a portion of thevalve needle 1 having a reduced diameter. On the outside, this firstsleeve 24 is likewise fitted with a very narrow guide play in the guide12 on the low-pressure side of the valve bore 3. Outside the valve bore3, a second sleeve 25 is provided, which in turn serves a chamfer 17 forreceiving the snap ring 16 disposed in a groove on the valve needle 1.Inserted between this first sleeve 24 and this second sleeve 25 is aU-shaped disk 26, which is axially guided in a bush 27. The bush 27 isprovided as a separate component from the valve housing 2 but may alsobe a component of the valve housing 2. To allow the snap ring 16 to beinstalled at a valve needle stroke that is less than the length of thechamfer 17, the sleeves 24 and 25 are slipped onto the valve needle 1;the snap ring 16 is installed; and then the U-shaped disk 26 is insertedbetween the first sleeve 24 and the second sleeve 25. Thus thedimensioning of this U-shaped disk 26 serves primarily to adjust thevalve stroke.

The valve bore 3 has one portion with a sealing diameter 29 that isidentical to the diameter of the guide 8 on the high-pressure side ofthe valve needle 1, so that when an outward-opening valve seat 23 isclosed, a complete high-pressure compensation can follow. For the sakeof a low- pressure compensation with the outward-opening valve seat 23closed, the first sleeve 24 has the same diameter as the sealing seat ofthe outward-opening valve seat 23.

As can be seen from FIG. 3, the first sleeve 24 has a slightly largerdiameter than the diameter of the guide 8 on the high-pressure side. Forthis reason, with an outward-opening valve seat 23 that is closed, onlya partial low-pressure compensation is possible, since accordingly thediameter of the first sleeve 24 is also somewhat greater than thediameter of the inward-opening valve seat 5.

The pressure in a chamber 30, from which the third conduit for thereturn branches off and which communicates with the control chamber 11when the outward-opening valve seat 23 is open, always presses the firstsleeve 24 and thus also the second sleeve 25, together with the U-shapeddisk 26, against the snap ring 16. When an outward-opening valve seat 23is closed, this is accomplished by the contrary force on thisoutward-opening valve seat 23. The variant embodiment of the 3/2-wayvalve shown in FIG. 3 may be embodied with or without an elastic element15. In the variant embodiment shown in FIG. 3, with the outward-openingvalve seat 23 closed, a complete hydraulic pressure compensation isachieved on the high-pressure side, since the sealing diameter of theoutward-opening valve seat 23 is equal to the diameter of the guide 8 onthe high-pressure side. At the same time, an at least partial hydrauliclow-pressure compensation can be attained by providing that the diameterof the outward-opening valve seat 23 is essentially equal to thediameter of the guide 12 on the low-pressure side.

FIG. 4 shows a third variant embodiment of a 3/2-way valve, which in itsessential characteristics is equivalent to the variant embodimentdescribed in conjunction with FIG. 3, with the distinction that thefirst sleeve 24 has the same diameter as the guide 8 on thehigh-pressure side, or in other words the same diameter as the sealingseat of the inward-opening valve seat 5 and the outward-opening valveseat 23. In this way, in a 3/2-way valve of this kind, both a completehigh-pressure compensation and a complete low-pressure compensation areassured.

The proposed variant embodiments may be employed in all valves thatswitch at high speed and are subjected to high pressure and are used inself-ignition internal combustion engines. The valve variants shown inFIGS. 1 through 4 are all distinguished by the fact that they can all beinstalled from the side of the guide 8 on the high-pressure side. As aresult, an actuator solidly connected to the valve needle 1 can beemployed, and this can be either an already preassembled magnet armatureunit or a piezoelectric adjuster. The variant embodiments shown in FIGS.1 through 4 of a valve for use in high-pressure hydraulics arehydraulically pressure-compensated; that is, the diameter of aninward-opening valve seat 5, for instance, matches a diameter of theguide 8 on the high-pressure side relative to the high-pressure side. Toattain a hydraulic low-pressure compensation, the diameters of a slideseat 19, or depending on the variant embodiment of an outward-openingvalve seat 23, are equivalent to the diameter of a guide 12 on thelow-pressure side of the valve needle 1.

LIST OF REFERENCE NUMERALS

-   1 Valve needle-   2 Valve housing-   3 Valve bore-   4 Actuator-   5 Inward-opening valve seat (I-valve seat)-   6 First conduit-   7 High-pressure chamber-   8 Guide on high-pressure side-   9 Sealing edge-   10 Second conduit-   11 control chamber-   12 Guide on low-pressure side-   13 Sleeve-   14 Rounded shoulder-   15 Elastic element-   16 Snap ring-   17 Chamfer-   18 Return-   19 Slide seat-   20 Third conduit (return)-   21 First sleeve-   22 Second sleeve-   23 Outward-opening valve seat (A-valve seat)-   24 First sleeve-   25 Second sleeve-   26 U-shaped disk-   27 Bush-   28 Sealing edge-   29 Sealing diameter-   30 Chamber

1-16. (canceled)
 17. In a valve for high-pressure hydraulics, comprisinga valve bore (3), provided in a valve housing (2), in which bore atleast one valve seat (5; 19; 23) is embodied that divides a guide (8) onthe high-pressure side of the valve bore (3) from a guide (12) on thelow-pressure side of the valve bore (3), and a valve needle (1)actuatable directly by an actuator (4), which needle is guided in thevalve bore (3) and has at least one sealing face (9; 28), which cancooperate with the at least one valve seat (5; 19; 23), the improvementwherein the valve needle (1) is constructed in multiple parts and, inthe region of the guide (12) on the low-pressure side, has at least onesleeve (13; 21, 22; 24, 25).
 18. The valve of claim 17, wherein the atleast one sleeve (13; 21, 22; 24, 25) is guided with a narrow elementplay in the guide (12) on the low-pressure side and on the valve needle(1).
 19. The valve of claim 18, wherein the at least one sleeve (13; 21,22; 24, 25) is axially braced on a shoulder (14) of the valve needle (1)by means of an elastic element (15).
 20. The valve of claim 19, furthercomprising a chamfer (17) on the at least one sleeve (13; 21, 22; 24,25) opposite the elastic element (15), and a snap ring (16) disposed inthe chamfer (17) and in a groove on the valve needle (1).
 21. The valveof claim 17, wherein said at least one sleeve comprises two sleeves (21,22), which are separated from one another and axially braced against oneanother by means of an elastic element (15).
 22. The valve of claim 18,wherein said at least one sleeve comprises two sleeves (21, 22), whichare separated from one another and axially braced against one another bymeans of an elastic element (15).
 23. The valve of claim 17, whereinsaid at least one sleeve comprises two sleeves (23, 24) separated fromone another by means of a U-shaped disk (26), and wherein the U-shapeddisk (26) is guided in a bush (27) that is connected to the valvehousing (2).
 24. The valve of claim 18, wherein said at least one sleevecomprises two sleeves (23, 24) separated from one another by means of aU-shaped disk (26), and wherein the U-shaped disk (26) is guided in abush (27) that is connected to the valve housing (2).
 25. The valve ofclaim 17, wherein the valve is embodied as a 2/2-way valve, with aninward-opening valve seat (5).
 26. The valve of claim 18, wherein thevalve is embodied as a 2/2-way valve, with an inward-opening valve seat(5).
 27. The valve of claim 19, wherein the valve is embodied as a2/2-way valve, with an inward-opening valve seat (5).
 28. The valve ofclaim 17, wherein the valve is embodied as a 3/2-way valve with aninward- opening valve seat (5) and with a slide seat (19).
 29. The valveof claim 17, wherein the valve is embodied as a 3/2-way valve with oneinward-opening valve seat (5) and with one outward-opening valve seat(23).
 30. The valve of claim 25, wherein, to compensate for thehydraulic forces engaging the valve needle (1) in the opening direction,the valve needle (1) has the same diameter at the guide (8) on thehigh-pressure side and at the guide (12) on the low-pressure side. 31.The valve of claim 29, wherein, to partially compensate for thehydraulic forces engaging the valve needle (1) in the opening direction,the valve needle (1) has a smaller diameter at the guide (8) on thehigh-pressure side than at the guide (12) on the low-pressure side. 32.The valve of claim 17, wherein the valve needle can be installed fromthe side of the guide (8) on the high-pressure side.
 33. The valve ofclaim 17, wherein a diameter at the inward-opening valve seat (5)corresponds to the diameter of the valve needle (1) inside the guide (8)on the high-pressure side, as a result of which the valve needle ispressure-compensated.
 34. The valve of claim 17, wherein, when the slideseat (19) is closed, a complete hydraulic high-pressure compensation isattained on the one hand because of matching diameters of the slide seat(19) and the diameter of the guide (8) on the high-pressure side, and acomplete hydraulic low-pressure compensation is attained because of thematching of the diameters of the slide seat (19) and the diameter of theguide (12) on the low-pressure side.
 35. The valve of claim 17, wherein,when the outward-opening valve seat (23) is closed, a complete hydraulichigh-pressure compensation is attained on the one hand because ofmatching diameters of the outward-opening valve seat (23) and thediameter of the guide (8) on the high-pressure side, and a completehydraulic low-pressure compensation is attained because of the matchingof the diameters of the outward-opening valve seat (23) and the diameterof the guide (12) on the low-pressure side.
 36. The valve of claim 23,wherein the sleeves (24, 25) are positioned and braced against a snapring (16) via the pressure relief or closing forces when theoutward-opening valve seat (23) is closed.